Electric lamp



Oct. 23, 1928.

- w. R. BURROWS ELECTRIC LAMP Filed Nov. 1. 1921 Inventor: William R. Burrows,

Hi5 Attow neg Patented Oct. 23, 1928.

UNETED S'FA'Ffi PATENT OFFICE.

WILLIAM R. BURROWS, OF NEWARK, NEW JERSEY, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC LAMP.

Application filed November 1, 1921.

My invention relates to incandescent lamps, and particularly to incandescent lamps having several filaments so arranged that by suitable connections any one or more of the filaments can be lighted at will.

One object of my invention is to provide an incandescent electric lamp with two or more concentrated filaments so arranged that when the lamp is focused in a signal lamp a headlight having a reflector. or in any similar device, all of the filaments will be equally in focus, and consequently the light from any one of the filaments will be projected and will be distributed in substantially the same way as the light from any other filament of the lamp.

Another object of my invention is to provide an improved lamp with filaments of different candle power all in focus and so arranged that any filament can be lighted at will.

The shape and distribution of the beam of light from signal lanterns, headlights, and similar devices is determined to a great extent by lenses designed to distribute light from a comparatively small or concentrated source at the focal center of a lens or reflector. In automobile headlights, for example, a concentrated and powerful beam of light is obtained from an incandescent lamp having a concentrated filament at the focal center of the reflector, and some form of lens or similar light distributing device is mounted in front of the reflector. To obtain a comparatively dim light for city driving an auxiliary filament of low candle power and out of focus has been used, but the dim light from this auxiliary filament and the bright light from the filament in focus are distributed differently by the lens, and for this reason among others, both filaments shouldbe as compact or concentrated and as near the focal center as possible.

My invention will best 'be understood in connection with the accompanying drawing,

, in which for purposes of illustration, I have shown some of the various forms in which it may be embodied. and in which Figure 1 is a View of a lamp embodying one form of my invention; Figure 2 is a View partly in section. showing in a reflector a lamp embodying another form of my invention and indicating the electrical connections by which either filament can be lighted at will, and

Serial No. 512,152.'

Figure 3 shows a lamp with two filaments of different candle power.

In the preferred embodiment of my inventi on shown in the drawings a substantially spherical lamp bulb 1 has a cylindrical base 2 of the usual bayonet type by which the lamp is supported and the electrical connections are made. The particular form of lamp shown has two filaments 3 and 4, which in accordance with my invention are made as concentrated as possible and of a length to give a beam of the desired width. These filaments, pref- 'erably made of coiled tungsten wire, are

mounted near the center of the bulb in such relative positions that if the lamp is placed with one filament in focus in a reflector having a focal center, the other filament will also be equally in focus. One of the filaments, such as filament 3, is preferably considerably curved or V-sha'ped, as shown in the drawing, and the other filament 4, is substantially perpendicular to the plane of the first filament, and extends through that plane at a point such that the middle points or vertices of both filaments are in the axis of the bulb and of the cylindrical base 2. If the filaments are of different candle power, as shown in Fig. 3, the curved filament 3 may conveniently be made the major filament and be of the greater candle power.

The reflectors used commercially are not perfect paraboloids, and a point of light which is anywhere within a short distance of the geometrical point which would be the focal point were the reflector geometrically perfect, is said to be at the focal center of the reflector, and is for all practical purposes in focus. If a filament, so concentrated that its incandescent portion is sufliciently small as compared with the reflector, is placed in a commercial paraboloid reflector, it produces on a screen or wall perpendicular to the axis of the reflector a spot of light having a shape and size dependent upon the reflector and its distance from the screen,'and also upon the shape and length of the filament and its position in the reflector. As the filament is moved back and forth along the axis of the. reflector, the size of the spot will vary, but a position of the filament can be found where that spot of light, regardless of its shape or absolute size, is of minimum diameter and has no dark spot in the center. When the filament is in that position it is said to be in len th of the curved filament.

or all practical purposes the light center of a concentrated V-shaped filament such as is generally used as a light source with parabolic reflectors is midway between'the middle pointsof the sides of the filament, and the light center of a concentrated are shaped filament which forms a half circle or less is midway between the middle point of the filament and the chord formed by a straight line joining the ends of the filament. The length of the sides of a V-shapcd filament or the curvature of an arc shaped filament can be made so great that its light center is'so far back of the middle point of the filament that another filament can be mounted with its light center substantially coincident with the light center of the first filament, and yet the two filaments will be so far apart that the danger of the filaments touching each other is very slight and the lamp is rugged and practical. curved, or may even be V-shaped with a more obtuse angle at the tip than the filament 8, as shown in Fig. 1, and may be mounted so that either its tip or middle point, or its light center, as shown in Figure 3, coincides with the light center of the major filament. Bot-h filaments are then equally in focus, and yet are so far apart that they do not touch even when the lamp is subjected to the severe ars and shocks encountered when used in 'an automobile headlight.

The filament 3 is mounted on the inner ends of two rigid leading-in wires 5 and 6, which mechanically support the filament and also supply it with current while the other filament 4 is supported by a third leading-in wire 7 and a branch or projection 8 of the leadingin wire 5, which is common to both filaments. In order that current may be supplied to either filament at will, the base 2 has its metal shell 9 connected to the leading-in wire 5, its contact 10 connected to leading-in wire 6 to supply current to the filament 3, and its contact 11 connected to leading-in wire 7 to supply current to the filament 4.

Current may be supplied to either filament at will in many ways, for example by means of circuits and a switch illustrated diagram matically in Figure 2, which shows the lamp in place in a parabolic reflector 12 having a bayonet socket 13 with a grounded metal shell and two contacts engaging the contacts 10 and 11 of the lamp and connected through The filament 4 may be slightly leading-in wire 5 and thenceto ground. The

other filament is lighted when the switch connects the other lead 15 to the battery, whereupon current flows through contact 11, the filament 4t, branch 8, and leading-in wire 5 to ground.

For use in automobile headlights the two filaments may be made of unequal candle power, as shown in Figure 3 in which case filament 3 is preferably the major filament of the greater candle power. In other cases the two filaments may to advantage be made of substantially e ual candle power to give nearly the same istribution and shape of beam, and to be of substantially equal candle power so that when one of the filaments breaks the other one can be switched on immediately, and no change or readjustment of the lamp with reference to the reflector is required, as both of the filaments are equally in focus. For use in headlights, signal light, and similar devices this form of lam is of value as it has in reserve a spare fi ainent properl focused and capable of replacing the other filament by the turn of a switch.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An incandescent lamp comprising a filament so curved that its light center is located at a distance from the middle point of the filament and in the plane of the filament between its sides, and a second filament mounted to extend through the plane of the curved filament with its vertex or middle 'point spaced away from the vertex or middle point of the curved filament sufficiently to make the light centers of the two filaments coincide.

2. An incandescent lamp comprising two independently operable concentrated coiled filaments mounted to lie in planes perpendicular to each other with the vertices or middle points of their heated portions in the line of intersection of said planes, one of said filaments being curved around the other suf' ficientl to space its vertex or middle point from t e middle point of the other filament so that the light centers of the two filaments coincide.

3. An incandescent lamp comprising a bulb, a base attached thereto, and apair of coiled concentrated filaments positioned within the bulb with their middle points in the axis ofsaid base, one of saidfilaments being curved to bring its light center between its middle point and the base, and the other filament being perpendicular to the plane of said first filament and to said axis and between said base and said first filament and far lll enough back from the middle point of said first filament to make its light center COlIlCldent with the light center of said first filament.

4. An incandescent lamp comprising two curved filaments shaped to have their light centers at different distances from their tips and mounted one within the other, and perpendicular to each other with their tips sub stantially in the line of intersection of the planes of said filaments but spaced apart along said line a distance substantially equal to the difference in the distances between the light centers and the tips of saidfilaments to make the light centers of said filaments coincide.

5. An incandescent electric light bulb for the purpose described comprising a single base and two independent filaments of unequal candle power and comparatively short length supported by said base, the filament which is furthest from said base being of V-shape with itsapex directed away from said base and located on the axis of the base, and the other filament lying crosswise be tween the legs of the V and spaced from the apex thereof a distance which is less than the height of such V.

6. An incandescent electric light bulb for the purpose described comprising a single base, a V-shaped high candle power filament of comparatively short length located upon the same axis with said base and having its apex turned away from said base, an independent low candle power filament having a V-shaped with its plane coinciding with the reflector axis and its apex substantially at the focal point, the other filament being located cross-wise of the first filament in the angle made by the legs thereof, the planes of said filaments being substantially perpendicular to each other, the second filament intersecting the axis of the reflector and spaced from the apex of the first filament sulficiently so as not to touch the same and the second filament be ing shaped to lie substantially within the surface which would be produced by revolvingthe first filament about the reflector axis.

8. The combination with a reflector having an axis and a focal point, of an incandescent electric light bulb comprising two independently usable V-shaped filaments arranged with their planes perpendicular to each other and their apices located on the reflector axis substantially at the focal point, said filaments being spaced apart so as not to touch each other, one of the same having each of its legs of wire which is wound in a fine coil and the other located crosswise in the angle made by said legs with the light centers of said filaments coinciding.

9. The combination with a headlight reflector having an axis and a focal point, of an electric light bulb comprising two independently usable filaments each of which is confined to a single plane and inside a triangular space, the planes of said filaments being perpendicular to each other and the vertex of each being located on said reflector axis and slightly spaced from each other. the outer filament consisting of a wire coil whose convolutions lie closely adjacent to each other so as to employ a comparatively large amount of wire, and the inner filament comprising a shorter length of wire having a higher resistance, the light centers of the filaments coinciding and lying on the axis of the reflector.

In witness whereof, I have hereunto set my hand this 29thday of October, 1921.

WILLIAM R. BURROWS. 

